Un-ignore /usr/lib/systemd/ in .gitignore with git repo on root filesystem

Actually, this is about un-ignoring any subdirectory that is grandchild to an ignored directory. Running Linux Mint 22.2 (based upon Ubuntu 24.04), and having a git repository on root filesystem to keep track of the computer s configuration, the vast majority of directories are ignored. One of the is /lib, however /lib/systemd/ should not be ignored, [...]